Lecture Xviii

THE TIDES, AND PLANETARY EVOLUTION 379

ILLUSTRATIONS

FIG. PAGE

1. ARCHIMEDES 8

2. LEONARDO DA VINCI 10

3. COPERNICUS 12

4. HOMERIC COSMOGONY 15

5. EGYPTIAN SYMBOL OF THE UNIVERSE 16

6. HINDOO EARTH 17

7. ORDER OF ANCIENT PLANETS CORRESPONDING TO THE DAYS OF THE WEEK 19

8. PTOLEMAIC SYSTEM 20

9. SPECIMENS OF APPARENT PATHS OF VENUS AND OF MARS AMONG THE STARS 21

10. APPARENT EPICYCLIC ORBITS OF JUPITER AND SATURN 22

11. EGYPTIAN SYSTEM 24

12. TRUE ORBITS OF EARTH AND JUPITER 25

13. ORBITS OF MERCURY AND EARTH 25

14. COPERNICAN SYSTEM AS FREQUENTLY REPRESENTED 26

15. SLOW MOVEMENT OF THE NORTH POLE IN A CIRCLE AMONG THE STARS 29

16. TYCHONIC SYSTEM, SHOWING THE SUN WITH ALL THE PLANETS REVOLVING ROUND THE EARTH 38

17. PORTRAIT OF TYCHO 41

18. EARLY OUT-DOOR QUADRANT OF TYCHO 43

19. MAP OF DENMARK, SHOWING THE ISLAND OF HUEN 45

20. URANIBURG 46

21. ASTROLABE 47

22. TYCHO'S LARGE SEXTANT 48

23. THE QUADRANT IN URANIBURG 49

24. TYCHO'S FORM OF TRANSIT CIRCLE 50

25. A MODERN TRANSIT CIRCLE 51

26. ORBITS OF SOME OF THE PLANETS DRAWN TO SCALE 60

27. MANY-SIDED POLYGON OR APPROXIMATE CIRCLE ENVELOPED BY STRAIGHT LINES 61

28. KEPLER'S IDEA OF THE REGULAR SOLIDS 62

29. DIAGRAM OF EQUANT 67

30. EXCENTRIC CIRCLE SUPPOSED TO BE DIVIDED INTO EQUAL AREAS 68

31. MODE OF DRAWING AN ELLIPSE 70

32. KEPLER'S DIAGRAM PROVING EQUABLE DESCRIPTION OF AREAS FOR AN ELLIPSE 71

33. DIAGRAM OF A PLANET'S VELOCITY IN DIFFERENT PARTS OF ITS ORBIT 72

34. PORTRAIT OF KEPLER 76

35. CURVE DESCRIBED BY A PROJECTILE 82

36. TWO FORMS OF PULSILOGY 87

37. TOWER OF PISA 91

38. VIEW OF THE HALF-MOON IN SMALL TELESCOPE 97

39. PORTION OF THE LUNAR SURFACE MORE HIGHLY MAGNIFIED 98

40. ANOTHER PORTION OF THE LUNAR SURFACE 99

41. LUNAR LANDSCAPE SHOWING EARTH 100

42. GALILEO'S METHOD OF ESTIMATING THE HEIGHT OF LUNAR MOUNTAIN 101

43. SOME CLUSTERS AND NEBULÆ 102

44. STAGES OF THE DISCOVERY OF JUPITER'S SATELLITES 103

45. ECLIPSES OF JUPITER'S SATELLITES 105

46. OLD DRAWINGS OF SATURN BY DIFFERENT OBSERVERS, WITH THE IMPERFECT INSTRUMENTS OF THAT DAY 111

47. PHASES OF VENUS 112

48. SUNSPOTS AS SEEN WITH LOW POWER 113

49. A PORTION OF THE SUN'S DISK AS SEEN IN A POWERFUL MODERN TELESCOPE 114

50. SATURN AND HIS RINGS 115

51. MAP OF ITALY 118

52. PORTRAIT OF GALILEO 126

53. PORTRAIT OF DESCARTES 148

54. DESCARTES'S EYE DIAGRAM 151

55. DESCARTES'S DIAGRAM OF VORTICES FROM HIS "PRINCIPIA" 152

56. MANOR-HOUSE OF WOOLSTHORPE 162

57. PROJECTILE DIAGRAM 170

58. } { 171 59. } DIAGRAMS ILLUSTRATIVE OF THOSE NEAR THE BEGINNING { 174 60. } OF NEWTON'S "PRINCIPIA" { 175 61-2. } { 175

63. PRISMATIC DISPERSION 182

64. A SINGLE CONSTITUENT OF WHITE LIGHT IS CAPABLE OF NO MORE DISPERSION 183

65. PARALLEL BEAM PASSING THROUGH A LENS 184

66. NEWTON'S TELESCOPE 186

67. THE SEXTANT, AS NOW MADE 187

68. NEWTON WHEN YOUNG 196

69. SIR ISAAC NEWTON 200

70. ANOTHER "PRINCIPIA" DIAGRAM 207

71. WELL-KNOWN MODEL EXHIBITING THE OBLATE SPHEROIDAL FORM AS A CONSEQUENCE OF SPINNING ABOUT A CENTRAL AXIS 219

72. JUPITER 221

73. DIAGRAM OF EYE LOOKING AT A LIGHT REFLECTED IN A DISTANT MIRROR THROUGH THE TEETH OF A REVOLVING WHEEL 238

74. FIZEAU'S WHEEL, SHOWING THE APPEARANCE OF DISTANT IMAGE SEEN THROUGH ITS TEETH 239

75. ECLIPSES OF ONE OF JUPITER'S SATELLITES 241

76. A TRANSIT INSTRUMENT FOR THE BRITISH ASTRONOMICAL EXPEDITION, 1874 243

77. DIAGRAM OF EQUATORIALLY MOUNTED TELESCOPE 245

78. ABERRATION DIAGRAM 250

79. SHOWING THE THREE CONJUNCTION PLACES IN THE ORBITS OF JUPITER AND SATURN 259

80. LORD ROSSE'S DRAWING OF THE SPIRAL NEBULA IN CANES VENATICI 269

81. SATURN 271

82. PRINCIPLE OF NEWTONIAN REFLECTOR 278

83. HERSCHEL'S 40-FOOT TELESCOPE 283

84. WILLIAM HERSCHEL 285

85. CAROLINE HERSCHEL 287

86. DOUBLE STARS 288

87. OLD DRAWING OF THE CLUSTER IN HERCULES 290

88. OLD DRAWING OF THE ANDROMEDA NEBULA 291

89. THE GREAT NEBULA IN ORION 292

90. PLANETARY ORBITS TO SCALE 297

91. DIAGRAM ILLUSTRATING PARALLAX 307

92. THE KÖNIGSBERG HELIOMETER 312

93. PERTURBATIONS OF URANUS 320

94. URANUS' AND NEPTUNE'S RELATIVE POSITIONS 325

95. METEORITE 333

96. METEOR STREAM CROSSING FIELD OF TELESCOPE 334

97. DIAGRAM OF DIRECTION OF EARTH'S ORBITAL MOTION 335

98. PARABOLIC AND ELLIPTIC ORBITS 340

99. ORBIT OF HALLEY'S COMET 341

100. VARIOUS APPEARANCES OF HALLEY'S COMET WHEN LAST SEEN 342

101. HEAD OF DONATI'S COMET OF 1858 343

102. COMET 344

103. ENCKE'S COMET 345

104. BIELA'S COMET AS LAST SEEN IN TWO PORTIONS 346

105. RADIANT POINT PERSPECTIVE 348

106. PRESENT ORBIT OF NOVEMBER METEORS 349

107. ORBIT OF NOVEMBER METEORS BEFORE AND AFTER ENCOUNTER WITH URANUS 351

108. THE MERSEY 355

109. CO-TIDAL LINES, SHOWING THE WAY THE TIDAL WAVE REACHES THE BRITISH ISLES FROM THE ATLANTIC 359

110. WHIRLING EARTH MODEL 364

111. EARTH AND MOON MODEL 365

112. EARTH AND MOON (EARTH'S ROTATION NEGLECTED) 366

113. MAPS SHOWING HOW COMPARATIVELY FREE FROM LAND OBSTRUCTION THE OCEAN IN THE SOUTHERN HEMISPHERE IS 369

114. SPRING AND NEAP TIDES 370

115. TIDAL CLOCK 371

116. SIR WILLIAM THOMSON (LORD KELVIN) 373

117. TIDE-GAUGE FOR RECORDING LOCAL TIDES 375

118. HARMONIC ANALYZER 375

119. TIDE-PREDICTER 376

120. WEEKLY SHEET OF CURVES 377

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